Describe the process a checksum algorithm uses to determine if an error has occurred [5 marks]
Answer:
- Before data is transmitted a checksum value is calculated [1]
- The checksum value is transmitted with the data [1]
- The receiver calculates the checksum value using the received data [1]
- The calculated checksum is compared to the transmitted checksum [1]
- If they are the same then there is no error otherwise an error has occurred [1]
How is check digit used in a barcode
- check digit is calculated from the barcode
- using an algorithm
- this check digit is added to the end of the value from barcode
- when the barcode is scanned, the check digit is recalculated
- using the same algorithm
- if the check digit is different and error has occurred
Program Counter
- Holds the memory address of the next instructions to be executed
- Increments by 1 as the fetch-decode-execute cycle runs
Memory Address Register
- Holds the memory address of where data or instructions are to be fetched from memory
Memory Data Register
Stores the data or instruction which has been fetched from memory
Current Instruction Register
Stores the instruction the CPU is currently decoding or executing
Accumulator
Stores the results of any calculations that have taken place in the Arithmetic Logic Unit (ALU)
Explain how an instruction is fetched using Von Neumann architecture
Answer
- The Program Counter (PC) holds the address/location of the next instruction to be fetched [1]
- The address held in the PC is sent to the Memory Address Register (MAR) [1]
The memory address is sent using the address bus [1] - The Program Counter is incremented [1]
- The instruction is sent from the address in memory to the Memory Data Register (MDR) [1]
- The instruction is transferred using the data bus [1]
- The instruction is sent to the Current Instruction Register (CIR) [1]
what is software
program used to operate hardware/software
why is secondary storage important
- allows for permanent data to be stored
- allows users to download apps
- for the creation of virtual memory
explain why a computer needs RAM
- To store data temporarily
- To store data currently in use
- To store software currently in use
- Data can be accessed faster (than secondary storage)
- To speed up the fetch stage (of the fetch-execute cycle)
Why is serial data transmission used
- The network may be spread over a long distance …
- … so it is more reliable
- Bits will be sent/arrive in sequence
- …so bits less likely to be skewed
- Less crosstalk/interference
- … so less likely to have errors
- The data may not need to be transmitted at a fast speed // data transmission speed of serial is adequate
- The cables in the network only use serial transmission
What is meant by a robot being automated
- robot can perform actions without human intervention
How does packet switching work
1) A large piece of data is broken down into packets.
2) Each packet is given a header.
3) the packets make its way to its destination
4) Routers control the routes taken by each packet
5) Once all the packets arrive, they are reordered correctly
how does checksums work
- Checksums are calculated using an algorithm and the value is added to the transmission
- The receiving device re-calculates the checksum and compares to the original
- If the checksums do not match, it is assumed an error has occurred
What is the purpose of a NIC
allows for a computer to connect to a network
What is a MAC
unique identifier given to devices, allowing for devices to communicate over a local area network (LAN)
3 characteristics of a robot
Any three from:
- It has a mechanical structure/framework
- It has electrical components
- It is programmable
- It can move
Explain how the firewall operates to help protect the network.
- Criteria can be set (for traffic)
- … such as a blacklist/whitelist (of IP addresses)
- It will examine traffic coming into the network
- It will check that the traffic meets the set criteria
- … and will reject it if it does not meet criteria
- Certain ports used by hackers can be blocked/closed
Advantages of low level languages
- Complete control over the system components
- Occupy less memory and execute faster
- Direct manipulation of hardware
Disadvantges of low level languages
- difficult to write and understand
- machine dependent
- more prone to errors
what is low-level languages
directly translates to machine code
what is high-level languages
uses English-like statements
advantages of high-level languages
- clear debugging
- easier to read and write
- one line of code can perform multiple commands
